1. Field of the Invention:
This invention relates to a radio-frequency matching transformer in the form of a coaxial line having at least two sections, each having a respective length and characteristic impedance.
2. Description of the Prior Art:
Such a matching transformer as above-noted is known in the field as a two-stage quarter-wave transformer. It consists of a wave guide the total length of which is equal to a half wavelength of the operating frequency .lambda..sub.o. It is subdivided into two quarter wave line sections, the different characteristic impedances of which are determined by the terminal impedances at the input and output between which the matching is to be produced. Since the length of this transformer is directly linked to the operating frequency, its use is limited by its respective dimensions to an operating frequency lying within a narrow band of frequencies. In addition, the geometry also determines the characteristic impedances just as, for example, with a coaxial line, so that transformers of different designs are required for different matching applications.
If, therefore, in a variable-frequency radio-frequency circuit the operating frequency and/or the impedance ratios change to a relatively great extent, a transformer inserted into the circuit will have to be replaced by another one with different geometry. This leads to a time-consuming conversion, especially in power circuits such as, for example, radio-frequency generators, which is associated with problems with regard to the electric contact between the sections of wave guide and the length compensation as a result of the change in operating frequency and in addition only permits discontinuous tuning.